Quantum Mechanical Calculation of Molecular Radii. I. Hydrides of Elements of Periodic Groups IV through VII

The fraction of the total electron density within a sphere having the empirical van der Waals radius is calculated for the atoms of eight elements, using Hartree-Fock atomic wavefunctions. The sphere is found to contain 97%–99% of the electron density, indicating that such calculations correlate well with atomic sizes. The procedure is extended to eight hydride molecules of the type AHn, with molecular size determined by the radius of the 98% contour as computed from published one-center SCF molecular wave-functions. The predicted molecular radii agree well with experimental values and support the usefulness of this method for describing effective molecular size.